The present invention relates to a high-resolution field emission display. More particularly, it relates to a high-resolution field emission display for applying a field emission device (or a field emission array) being an electron source element to a flat panel display device.
Field emission display devices are manufactured by making a vacuum-packaging between a lower plate having field emitter arrays and a upper plate having phosphors positioned within a small distance, e.g., 2 mm from the lower plate. The field emission display device generates cathode luminescence by colliding electrons emitted from field emitters of the lower plate against phosphors of the upper plate, thereby achieving an image display. Recently, the field emission display devices have been widely developed as a flat panel display substituting for conventional cathode ray tube (CRT).
The field emitter serving the most important function of the lower plate of the field emission display device has different electron emission efficiency according to the structure, emitter material, and emitter shape. At present, there are two kinds of field emission elements, those are, diode type device comprised of a cathode (or emitter) and an anode, and triode type device comprised of a cathode, a gate and an anode. Several materials such as metal, silicon, diamond, diamond-like carbon, or carbon nanotube have been used as the emitter material. In general, metal and silicon are used for the triode type device, and diamond-like carbon or carbon nanotube are used for the diode type structure. The diode type field emitter has a disadvantage in the control characteristic of the electron emission and high voltage driving characteristic, as compared to the triode type field emitter. But, the manufacturing process of the diode type field emitter is relatively easier than that of the triode type field emitter, so that large-sized devices can be easily manufactured.
In the meantime, field emission display device is classified into simple matrix panel type and active matrix panel type, according to the pixel arrangement of the lower plate in a matrix format. The simple matrix field emission display forms each pixel with a field emitter array only, whereas the active matrix field emission display forms each dot pixel with a field emitter array and a semiconductor device (mainly, a transistor) controlling the field emission current of the field emitter array.
FIGS. 1-3 are cross-sectional views illustrating one dot pixel of a conventional field emission display device. FIG. 1 is a cross-sectional view illustrating a dot pixel structure of a simple matrix field emission display device consisting of a conventional triode type field emitter array.
Referring to FIG. 1, the conventional field emission display device includes a lower plate and a upper plate facing to each other, wherein the lower plate and the upper plate are vacuum-packaged. The lower plate includes a glass substrate 101, a cathode electrode 102 made of metal deposited on the glass substrate 101, a resistance layer 103 made of doped amorphous silicon on the cathode electrode 102, a cone-type field emission tip 104 made of a metal (mainly, molybdenum), which is partially deposited on the resistance layer 103, and a gate insulation layer 105 and a gate electrode 106 which are used to apply electric field to the field emission tip 104. The upper plate includes a glass substrate 121, a transparent electrode 122 formed on the glass substrate 121, a red, green, or blue phosphor 123 partially formed on the transparent electrode 122.
The field emission display of FIG. 1 has an advantage of inducing reliable field emission at a relatively low voltage (generally, 80 V), but the field emission display has a limitation in manufacturing field emission tips in large-sized plate and requires a high field emission voltage.
FIG. 2 is a cross-sectional view illustrating a dot pixel structure of a simple matrix field emission display device comprised of a conventional diode type field emission element.
Referring to FIG. 2, a conventional field emission display device includes a lower plate and a upper plate facing to each other, wherein the lower plate and the upper plate are vacuum-packaged. The lower plate includes a glass substrate 201, a cathode electrode 202 made of metal deposited on the glass substrate 201, a resistance layer 203 made of doped amorphous silicon on the cathode electrode 202, and a diode type field emission film 204 made of carbon nanotube, which is partially formed on the resistance layer 203. The upper plate includes a glass substrate 221, a transparent electrode 222 formed on the glass substrate 221, a red, green, or blue phosphor 223 partially formed on the transparent electrode 222.
The field emission display device of FIG. 2 has a simple structure and facilitates the fabrication process, but the field emission display device requires a high field emission voltage and has unstable field emission characteristic and relating low an uniformity and reliability.
FIG. 3 is a cross-sectional view illustrating a dot pixel structure of an active matrix field emission display device comprised of a conventional diode type field emission element and a polycrystalline silicon thin film transistor (TFT).
Referring to FIG. 3, a conventional field emission display device includes a lower plate and a upper plate facing to each other, wherein the lower plate and the upper plate are vacuum-packaged. The lower plate includes a glass substrate 301; a TFT""s channel 302 made of undoped polycrystalline silicon; TFT""s source 303 and drain 304 made of doped polycrystalline silicon on both sides of the TFT""s channel 302; a gate insulation layer 305 made of silicon oxide (SiO2) layer, which is deposited on the channel 302, the source 303 and the drain 304 of TFT; a first gate 306 which is formed on some parts of the gate insulation layer 305 to vertically overlap with some portions of the TFT""s source 303 and the TFT""s channel 302, and not overlap with the TFT""s drain 304; a passivation insulation layer 307 made of a silicon oxide layer, which is formed on the first gate 306; a second gate 308 which is formed on some portions of the passivation insulation layer 307 to vertically overlap with some parts of the TFT""s channel 302 and the TFT""s drain 304; and a diode type field emission film 309 formed of carbon nanotube, which is formed to be electrically connected to the TFT""s drain 304 by partially removing the gate insulation layer 305 and the passivation insulation layer 307 that are formed on the TFT""s drain 304. The upper plate includes a glass substrate 321, a transparent electrode 322 formed on the glass substrate 321, a red, green, or blue phosphor 323 partially formed on the transparent electrode 322.
The field emission display device of FIG. 3 can remarkably restrict the cross-talk a display signal because each dot pixel is electrically isolated by a polycrystalline silicon thin film transistor. In addition, since the field emission current is controlled by the polycrystalline silicon thin film transistor, the field emission display device can be driven at a low voltage and can achieve very stable electron emission characteristic. However, the field emission display of FIG. 3 has a difficulty in manufacturing a large-sized field emission display device because a process for making a polycrystalline silicon thin film transistor should be added to the manufacturing process of the field emission display device of FIG. 3, and therefore the production cost becomes very expensive.
In the meantime, conventional field emission displays shown in FIGS. 1-3 have a difficulty in manufacturing a high-resolution display device, because spreading of electron beam occurs when the electron beam emitted from the field emission element is applied on the phosphor. Accordingly, in order to prevent such spreading of electron beam, an additional focusing electrode should be needed to the conventional field emission display devices.
Accordingly, the present invention is directed to a high-resolution field emission display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
It is an object of the present invention to provide a high-resolution field emission display which replaces a polycrystalline silicon thin film transistor used as a control/switching element of a field emission current in an active matrix field emission display device with an amorphous silicon thin film transistor (TFT). By doing so, it is impossible to make a large-sized active matrix field emission display device, and restrict TFT""s optical leakage current due to the photoelectric characteristic of amorphous silicon and obtain an effect of focusing the emitted electron beam.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, includes a field emission display including a lower plate having electron source dot pixels formed a diode type field emission film in a matrix arrangement and an upper plate having phosphor dot pixels, the lower plate and the upper plate being vacuum packaged in parallel positions, and including a transistor for driving field emission of each electron source dot pixel, and further including an electron beam focusing electrode/light-shading film being arranged to partially enclose the region of the lower plate where the field emission film is formed, and focusing the electron beam emitted from the electron source dot pixel so as to accurately direct the electron beam to the phosphor dot pixel in the upper plate, and preventing the light emitted from the phosphor of the upper plate from being irradiated on the channel of the transistor of the lower plate.
In another aspect, a transistor is provided that is suitable to a field emission display including a lower plate having a field emission film being an electron source and a upper plate having a phosphor collided by an electron beam emitted from the field emission film, the transistor includes: a substrate properly used as the lower plate; a gate made of a metal thin film formed on a part of the lower plate; a gate insulation layer made of a silicon nitride film deposited on the lower plate including the gate; a channel made of amorphous silicon deposited on the gate insulation layer and positioned over at least a part of the gate; a source made of doped amorphous silicon deposited on the channel and positioned over at least a part of the gate; a drain made of doped amorphous silicon deposited on the channel and having a lateral side opposing a lateral side of the source and positioned at a location offset from the gate in a lateral direction; a source electrode made of a metal thin film deposited on the source; and a drain electrode made of a metal thin film deposited on the drain, wherein the drain electrode is extended to provide a substrate for forming the electron source dot pixel, and is deposited on the lower plate
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the scheme particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.